This invention relates to a curable fluoropolyether base rubber composition which cures into products having improved compression set as well as water repellency, oil repellency, solvent resistance, chemical resistance and weather resistance and finding typical use as O-rings.
Silica fillers including dry silica (known as fumed silica) and wet silica (known as precipitated silica) are commonly used in silicone rubber for reinforcement purposes and often surface treated to be hydrophobic. It is known that blending such hydrophobized silica filler in the curable fluoropolyether base rubber can remarkably improve the mechanical properties of the cured product thereof. The blending of hydrophobized silica filler provides fluoropolyether base rubber compositions with a good balance of heat resistance, chemical resistance, solvent resistance, water repellency, oil repellency, and weather resistance. The resultant compositions perform well in most applications.
Albeit satisfactory performance in most applications, the fluoropolyether base rubber compositions are required to have a lower compression set in the application where they are molded into O-rings or the like. An improvement in compression set properties remains outstanding.
An object of the invention is to provide a curable fluoropolyether base rubber composition which has improved compression set as well as heat resistance, chemical resistance, solvent resistance, water repellency, oil repellency, and weather resistance.
The present invention provides a curable fluoropolyether base rubber composition comprising
(A) 100 parts by weight of a linear fluoropolyether compound containing at least two alkenyl groups in a molecule and having a perfluoroalkyl ether structure in its backbone,
(B) 10 to 40 parts by weight of a silica filler having a specific surface area of at least 100 m2/g and a vinyl content of 1xc3x9710xe2x88x923 to 2xc3x9710xe2x88x922 mol/100 g, which has been surface hydrophobized,
(C) an effective amount to cure component (A) of an organosilicon compound having at least two hydrogen atoms each bound to a silicon atom in a molecule, and
(D) a catalytic amount of a hydrosilylation catalyst. This fluoropolyether base rubber composition cures into products having improved compression set as well as heat resistance, chemical resistance, solvent resistance, water repellency, oil repellency, and weather resistance.